The PWT designed and installed Gas Gravel Wiping System is for
galvanising operations that require a thicker layer of zinc at wire
speeds normally in the range of DV 120 to DV 160.

Essentially the wire passes through a loose gravel bed in a
controlled atmosphere consisting of hydrogen sulphide and a reducing gas
for Class 3 Coating. Out of this a zinc sulphide layer (shiny,
non-oxidised coating) is formed.

The zinc sulphide layer has greater tensile strength and elasticity
than zinc oxide and allows a fast withdrawal of the wire without a
break-down of the skin.